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Earth science
Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth.[1] It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth science. There are four major disciplines in earth sciences, namely geography, geology, geophysics and geodesy. The major disciplines use physics, chemistry, biology, chronology and mathematics to build a quantitative understanding of the principal areas or spheres of the Earth system.
Earth's spheresEarth science generally recognizes 4 spheres, the lithosphere, the hydrosphere, the atmosphere, and the biosphere.[2] These correspond to rocks, water, air, and life. Some practitioners include the cryosphere (ice) as a distinct portion of the hydrosphere and the pedosphere (soil) as an active, intermixed sphere as part of Earth's spheres. 
Lava flows from the K?lauea volcano into the ocean on the Island of Hawaii.
Earth's interior
Plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of energy transformations in the Earth's crust.[10] Beneath the earth's crust lies the mantle which is heated by the radioactive decay of heavy elements. The mantle is not quite solid and consists of magma which is in a state of semi-perpetual convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics.[11][12][13][14] Plate tectonics might be thought of as the process by which the earth resurfaces itself. Through a process called spreading ridges (or seafloor spreading), the earth creates new crust by allowing magma underneath the lithosphere to come to the surface where it cools and solidifies--becoming new crust, and through a process called subduction, excess crust is pushed underground--beneath the rest of the lithosphere--where it comes into contact with magma and melts--rejoining the mantle from which it originally came.[12][14][15] Areas of the crust where new crust is created are called divergent boundaries, and areas of the crust where it is brought back into the earth are called convergent boundaries.[16][17] Earthquakes result from the movement of the lithospheric plates, and they often occur near covergent boundaries where parts of the crust are forced into the earth as part of subduction.[18] Volcanoes result primarily from the melting of subducted crust material. Crust material that is forced into the Asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface--giving birth to volcanoes.[12][18] Earth's electromagnet<gallery> Image:Electromagnetism.svg|Current flowing around an iron core creates an electromagnet. Image:CampoMagnetico.png|Earth is an electromagnet. </gallery> An electromagnet is a magnet that is created by a current that flows around a soft-iron core.[19] The earth has a soft iron core surrounded by semi-liquid materials from the mantle that move in continuous currents around the core;[20] therefore, the earth is an electromagnet. This is referred to as the dynamo theory of earth's magnetism.[21][22] The fact that earth is an electromagnet helps with the earth's maintenance of an atmosphere suitable for life. Atmosphere
The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. It is compressed on the day (Sun) side due to the force of the arriving particles, and extended on the night side. (Image not to scale.) The earth is blanketed by an atmosphere consisting of 78.0% nitrogen, 20.9% oxygen, and 1% Argon.[23] The atmosphere has five layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere; and 75% of the atmosphere's gases are in the bottom-most layer, the troposphere.[23] The magnetic field created by mantle's internal motions produces the magnetosphere which protects the earth's atmosphere from the solar wind.[24] It is theorized that the solar wind would strip away earth's atmosphere in a few million years were it not for the earth's electromagnet. And since earth is 4.5 billion years old,[25] earth would not have an atmosphere by now if there were no magnetosphere. The atmosphere is composed of 78% nitrogen and 21% oxygen. The remaining one percent contains small amounts of other gases including CO2 and water vapors.[23] Water vapors and CO2 allow the earth's atmosphere to catch and hold the sun's energy through a phenomenon called the greenhouse effect.[26] This allows earth's surface to be warm enough to have liquid water and support life. In addition to storing heat, the atmosphere also protects living organisms by shielding the earth's surface from cosmic rays. Note that the level of protection is high enough to prevent cosmic rays from destroying all life on Earth, yet low enough to aid the mutations that have an important role in pushing forward diversity in the biosphere. MethodologyLike all other scientists, Earth scientists apply the scientific method. They formulate hypotheses after observing events and gathering data about natural phenomena, and then they test hypotheses from such data. A contemporary idea within earth science is uniformitarianism. Uniformitarianism says that "ancient geologic features are interpreted by understanding active processes that are readily observed". Simply stated, this means that features of the Earth can be explained by the actions of gradual processes operating over long periods of time; for example, a mountain need not be thought of as having been created in a moment, but instead it may be seen as the result of continuous subduction, causing magma to rise and form continental volcanic arcs. Partial list of the major Earth Science topicsAtmosphereBiosphereHydrosphereLithosphere or geosphere
PedosphereSystemsOthersNotes and referencesReferences
See also
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